1. Field of the Invention
The invention relates to a tracking access control method and device for an optical storage medium drive, and more particularly, to a tracking access control method and device for exerting a brake force on a sled according to a sliding speed of the sled relative to an optical storage medium.
2. Description of the Prior Art
In modern society, there has been an increase in the use of optical storage medium, such as compact discs, for recording a huge amount of high-density digital information. The optical storage medium has advantages of lightweight, small size, and large capacity for storing data. Meanwhile, a reproducing apparatus, referred to as an optical storage medium drive, is indispensable for reading out information on optical storage medium. With the demand of high access speed for the optical storage medium, the rotation rate of the optical storage medium drive gradually increased. Furthermore, in order to read high-density data rapidly, to precisely read information from the optical storage medium is necessary. Therefore, developing a precise control system for the optical storage medium drive has become an important topic.
Please refer to FIG. 1. FIG. 1 is a schematic diagram illustrating the inner construction of an optical storage medium drive 10. For clarity of illustration, unrelated parts of the optical storage medium drive 10 are omitted. The optical storage medium drive 10 is used to read data stored in an optical storage medium 12. Also, only a portion of the optical storage medium 12 is shown in FIG. 1 for clarity. Data is stored in tracks of the optical storage medium 12. Three tracks 30A, 30B, 30C are shown in FIG. 1. Additionally, tracks, with data stored thereon, can be divided a radial direction of the optical storage medium 12 into a plurality of sectors on the tracks.
The optical storage medium drive 10 comprises a motor 14 for rotating a rotatable base 16 and further driving the optical storage medium 12 disposed on the rotatable base 16. The optical storage medium drive 10, used for accessing data on the optical storage medium 12, has a sled 20 capable of sliding left and right along a slide 18, i.e., along direction 22. A control circuit 29 controls the sliding movement of the sled 20. An actuator 24 is installed on the sled 20 to slide left and right along direction 26 within a small range on the sled 20. An optical pickup head 28 is fixed on the actuator 24 and can direct light beam, such as laser beam, to shine onto bottom surface of the optical storage medium 12. After the incident light beam is modulated by tracks of the optical storage medium 12 and reflected back to the optical pickup head 28, the optical storage medium drive 10 can thus read data stored on the optical storage medium 12.
When the optical storage medium drive 10 reads data stored in different tracks of the optical storage medium 12, a track crossing operation is carried out. For example, when the optical storage medium drive 10 desires to read data in the track 30C after data stored in the track 30A is read, the optical pickup head 28 is moved at high speed by the sled 20 and stopped in the vicinity of the track 30C. Then, the optical pickup head 28 is finely moved by the actuator 24 to the desired track 30C so as to accurately read data in the track 30C.
In the prior method for controlling the sled 20, when the sled 20 is moved from initial position to a target position, an accelerated force is exerted on the sled 20 so as to accelerate the sled 20 to move toward the target position. Meanwhile, a tracking access process is performed during the movement so as to identify the current position of the sled 20. When the sled 20 approaches the target position, a brake force in the opposite direction of the accelerated force is exerted on the sled 20 so as to decelerate the sled 20. Meanwhile, the tracking access process is also performed to lock the sled 20 at the target position.
In the prior control method, the magnitude and the duration of the brake force exerted on the sled 20 are preset at fixed values. Under this situation, when the speed of the sled 20 sliding from the initial position to the target position is too high, the brake force cannot decelerate the sled 20 to an appropriate speed within a finite period. Finally, the sled 20 has possibility of passing the target position due to the high speed that cannot be decelerated in time. When the target position is missed, the sled 20 has to take time in the subsequent calibration process to reach the target position. On the other hand, when the speed of the sled 20 in sliding is too slow, the brake force decelerates the sled 20 and causes the sled 20 to be stopped too early. Then, the sled 20 also needs to take time to reach the target position by the fine movement of the actuator 24. Therefore, whenever the sled 20 is moved too quickly or slowly, the prior control method is required to take time to lock the sled 20 to the target position. This cannot meet the high-speed demand of the optical storage medium drive 10 for accessing information in the optical storage medium 12.
Furthermore, since the accelerated force exerted by an exerting mechanism, e.g., a servo device, of each of the optical storage medium drives 10 may be either large or small, depending on the differences in the hardware fabrication, the prior control method that provides fixed brake force cannot be performed well in optical storage medium drives 10 with the different accelerated forces. These differences also cause the prior optical storage medium drives 10 to take time for locking the sleds 20 to the target positions. Thus, the read efficiency of the optical storage medium drive 10 is substantially decreased.